1. Field of the Invention
The present invention relates to a diaphragm gas meter which meters a gas flow rate or amount, and in particular to a diaphragm gas meter which can prevent pressure fluctuation from occurring to reduce pressure loss and can be reduced in size.
2. Description of the Related Art
FIGS. 7A and 7B are front views which schematically show an ordinary diaphragm gas meter 100. The diaphragm gas meter 100 is provided with a gas meter housing or main body 101, and the gas meter housing 101 is constituted by combining an upper case 102 and a lower case 103. The upper case 102 is provided with a gas inflow port 104 and a gas outflow port 105. The lower case 103 is provided with a measuring chamber 106, and the measuring chamber 106 is provided with a measuring diaphragm 107.
The measuring diaphragm 107 has a function which reciprocates according to gas pressure flowed from the gas inflow port 104 of the gas meter housing 101. The reciprocation of the measuring diaphragm 107 is transmitted to an interlocking mechanism 108 constituted of a crank mechanism and a valve mechanism accommodated in the upper case 102 via a wing shaft (not shown). The interlocking mechanism 108 is interlocked with an integration display section 109, on which an integrated value of an inflow gas amount calculated based upon motion of the measuring diaphragm 107.
The crank mechanism is provided with a large elbow metal and a small elbow metal. Reciprocating motion of the measuring diaphragm 107 is converted to a crank motion of the crank mechanism by rotational motion of the wing shaft. Motion of the crank mechanism is interlocked with the integration display section 109 via the interlocking mechanism 108. Such a gas meter is disclosed, for example, in Jpn. Pat. Appln. KOKAI Publication No. 5-164589.
The measuring diaphragm 107 is made of a flexible member such as a rubber. A front shape of the measuring diaphragm 107 is a circular shape as shown in FIG. 7A, or it is a rectangular shape or a rectangular shape with four corners rounded (hereinafter, “rounded rectangular shape”), as shown in FIG. 7B. A diaphragm plate (not shown) is attached to a central portion of the measuring diaphragm 107. An outer peripheral portion of the measuring diaphragm 107 is fixed to the lower case 103 forming the measuring chamber 106 in an air tight manner. The diaphragm plate is coupled to a wing shaft via a rotational arm (not shown). The measuring diaphragm 107 reciprocates according to gas pressure of gas which alternately flows into sections of the measuring chamber 106 which are defined on a surface side and a back surface side of the measuring diaphragm 107. The reciprocation is transmitted from the diaphragm plate to the wing shaft via the rotational arm as rotational motion.
In the measuring diaphragm 107 in the conventional diaphragm gas meter 100, however, rucks occur at four corners in one with a rectangular shape or a rounded rectangular shape in some cases, as shown in FIG. 7B. When stretching/shrinking of the rucks becomes resistive, smooth reciprocation of the measuring diaphragm is obstructed, which causes pressure fluctuation, resulting in large windage. When rucks occur in the measuring diaphragm, the measuring diaphragm can not always achieve constant measuring to a volume (one cycle volume) of gas which should be originally constant, which causes such a problem that a stable measuring performance required as a gas meter can not be attained.
In view of these circumstances, in order to solve the problem about the rucks occurring in the measuring diaphragm, a circular measuring diaphragm 107 has been developed, as shown in FIG. 7A. Rucks hardly occur in the circular measuring diaphragm 107 at a time of reciprocation, so that reciprocation of the measuring diaphragm is conducted smoothly. However, the circular measuring diaphragm 107 becomes smaller in area of a diaphragm front than the rectangular diaphragm or the rounded rectangular diaphragm due to a limited space in the gas meter, and one cycle volume of the former is therefore smaller than that of the latter.
Accordingly, when the amounts of gases passing through a gas meter with the former measuring diaphragm and a gas meter with the latter measuring diaphragm are equal to each other, namely, the flow rates in the both are equal to each other, the former measuring diaphragm is faster in diaphragm motion than the latter measuring diaphragm. In other words, the number of reciprocating motions in the former measuring diaphragm increases necessarily. The increase in the number will affect pressure loss of gas or durability of the gas meter adversely. When a discharge volume of gas in use of the circular measuring diaphragm is tried to be equal to that in use of the rectangular or rounded rectangular measuring diaphragm, the gas meter must be increased in height and width, which results in difficulty in shape compacting.